A so-called hybrid vehicle that is driven by an internal combustion engine and an electric motor receives attention. When the hybrid vehicle decelerates, the electric motor functions as an electric generator to perform an electric power regeneration (hereinafter, also simply referred to as a regeneration) and storage the electric power. The stored electric power is used for generating driving force, for example, when the vehicle accelerates or runs.
Some hybrid vehicles have a gear box configured to automatically shift gears. Hereinafter, the gear box is also referred to a transmission.
In this case, a clutch configured to connect the power or cut the connection of the power can be provided between the internal combustion engine and the electric motor.
FIGS. 5A and 5B are time charts for showing the rotational speeds of the electric motor and the internal combustion engine, and the torque of the electric motor and the torque that the driver requests to be generated (hereinafter, referred to as a driver's request torque) when the vehicle shifts from the state in which the vehicle runs only by the driving force of the electric motor (hereinafter, referred to as an EV driving state) to the state in which the vehicle runs only by the driving force of the internal combustion engine (hereinafter, referred to as an engine driving state).
In FIG. 5A, the rotational speed is shown on the vertical axis, and the time is shown on the horizontal axis. In FIG. 5A, the solid line denotes the rotational speed of the internal combustion engine, and the alternate long and short dash line denotes the rotational speed of the electric motor.
In FIG. 5B, the torque is shown on the vertical axis, and the time is shown on the horizontal axis. In FIG. 5B, the dash line denotes the driver's request torque, and the alternate long and short dash line denotes the torque of the electric motor.
The vehicle is started only by the driving force (torque) of the electric motor at a time t1, the shift from the EV driving state to the engine driving state is started at a time t2, and the clutch is engaged so that the state is shifted to the engine driving state during the time from the time t2 to a time t3.
Because the torque of the electric motor is rapidly dropped to zero and the clutch is engaged at the time t2, a period during which the rotational speed of the electric motor does not increase develops from the time t2 to the time t3 as illustrated in FIG. 5A when the rotational speed of the internal combustion engine is lower than the rotational speed of the electric motor.
Some parallel hybrid vehicles in the past include a battery temperature sensor for detecting the state of the battery, an HVECU, a vehicle speed sensor for detecting the state of the vehicle, an engine rotational speed sensor, an accelerator pedal opening sensor, and an FI/AT/MGECU for changing the request values of the engine and the motor based on the accelerator pedal opening and determining from the state of the vehicle whether the supply of fuel to the engine should be stopped. When the vehicle is decelerating and the accelerator pedal opening is equal to or less than a predetermined opening, the fuel cut state is maintained and the target torque found based on the accelerator pedal opening is controlled by an MOTECU until the accelerator pedal opening increases to the predetermined opening (for example, see Patent Literature PTL1).